OFFSET
1,1
COMMENTS
Numbers b such that A255920(b) = 4.
LINKS
Felix Fröhlich, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Wieferich Prime
MATHEMATICA
wp[b_] := Count[Complement[Prime[Range[PrimePi[b]]], FactorInteger[b][[All, 1]] ], p_ /; Divisible[b^(p - 1) - 1, p^2]];
Select[Range[2, 1200], wp[#] == 4&] (* Jean-François Alcover, Nov 26 2017 *)
PROG
(PARI) is(n) = my(i=0); forprime(p=1, n-1, if(Mod(n, p^2)^(p-1)==1, i++); if(i > 4, return(0))); i==4
(Sage) [b for b in range(3, 1107) if len([p for p in range(2, b) if is_prime(p) and mod(b, p^2)^(p-1)==1])==4] # Danny Rorabaugh, Mar 31 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Felix Fröhlich, Mar 23 2015
STATUS
approved